This invention relates to the field of polymer films, particularly thermotropic liquid crystalline polymer ("LCP") films.
A variety of thermotropic liquid crystal polymers and films made therefrom are known in the art. For example, U.S. Pat. No. 4,161,470 discloses a polyester of 6-hydroxy-2-naphthoic acid and p-hydroxy benzoic acid capable of undergoing melt processing, U.S. Pat. No. 4,184,996 discloses melt processible thermotropic wholly aromatic polyesters, and U.S. Pat. No. 4,279,803 discloses a polyester of phenyl-4-hydroxybenzoic and 4-hydroxybenzoic acid and/or 6-hydroxy-2-naphthoic acid.
Other patents disclosing LCPs include U.S. Pat. Nos. 3,991,013, 3,991,014, 4,057,597, 4,066,620, 4,067,852, 4,075,262, 4,083,829, 4,093,595, 4,118,372, 4,130,545, 4,219,461, 4,267,289, 4,276,397, 4,330,457, 4,339,375, 4,341,688, 4,351,917, 4,351,918, 4,355,132, 4,355,133, 4,371,660, 4,375,530, 4,460,735, 4,460,736, 4,473,682, 4,489,190, 4,581,443, 4,671,969, 4,673,591, 4,726,998, 4,752,643, 4,770,777, 4,772,421, 4,857,255, 4,898,924, and 4,913,867.
The disclosures of all the aforementioned patents are herein incorporated by reference.
Liquid crystalline polymer film or sheet has a number of well-known applications, including some that involve a lamination process. Examples include tape winding composite structures, cross lamination to provide balanced mechanical properties or thick structures, metal lamination for circuits, or lamination of circuit/dielectric layers for multilayer circuit boards.
Due to the particular molecular structure of thermotropic liquid crystal polymers, LCP film can be molecularly oriented in the melt phase, uniaxially, biaxially, or otherwise. After the extruded LCP cools and solidifies, the molecular orientation is maintained, resulting in a film having anisotropic properties, such as enhanced mechanical properties in the direction(s) of orientation, e.g. high strength and stiffness.
LCP films may be laminated together, or laminated to other materials. Typically, to obtain good adhesion this process involves heating the LCP until it melts and flows to produce a bond between the laminated layers. Unfortunately, when an LCP is heated above its softening or melting point its molecular orientation and overall shape tend to change as the polymer flows. For this reason, it is difficult to laminate a film of LCP while keeping constant its orientation and properties.
U.S. Pat. No. 4,384,016 discloses a multiaxially oriented laminate composed of uniaxially oriented LCP sheets. The sheets are thermally bonded together with their orientation in different directions to provide multiaxially LCP properties.